Apart from the use of computers to control movement increments, machine tools have changed little in their operating principles in the past hundred years. Modern machine tools rely upon the provision of a series of movement axes, stacked one after another, enabling an operator to effect independent movement in each axis. To keep such an arrangement stiff requires heavy and bulky mechanisms which in turn constrains the freedom of available movement. The pinnacle of modern day machine tool technology is the computer numerically controlled (CNC) five-axis mill which enables smoothly flowing curved surfaces to be produced. The cost of such CNC machines is typically of the order of hundreds of thousands of pounds, excluding the cost of essential complex computer aided manufacturing (CAM) software.
Computer aided design (CAD) systems have been developed and are widely used which far outstrip the abilities of machine tool based CAM systems, and there is a recognised need to bridge this gap and enable companies more readily to translate their CAD developments into CAM hardware. The product that hitherto has come closest to satisfying this requirement, at least for model making applications, is the stereolithography (SLA) system developed by 3D Systems Inc. In this SLA system models are "grown" in a vat of photo-polymer by scanning cross-sections with an ultraviolet laser. The technique offers poor initial surface finish, uses a very expensive and specialised material, is very slow, and furthermore is very expensive to install; despite these serious limitations the interest that has been stimulated by the SLA system has led to the development of several equivalent processes utilizing different chemical reactions by major league international industrial corporations. Other high technology proposals reportedly under development include the fusing of plastics beads by the heat of a laser beam and the deposition of plastics from molten droplets. The development of such sophisticatedly complex systems, despite their self-evident disadvantages, is a clear indication that industry has turned its back on the possibility of conventional machine tools being developed to such a level of sophistication as to enable the goal of what might be called desk-top manufacturing to be achieved.